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Home , Pinus lambertiana, Pinus ponderosa

Dougl. Sugar Pine family Bohun B. Kinloch, Jr. and William H. Scheuner

Called “the most princely of the genus” by its dis- 335 to 1645 m (1,100 to 5,400 ft) coverer, , sugar pine (Pinus Zamber- Sierra 610 to 2285 m (2,000 to 7,500 ft) tiana) is the tallest and largest of all , common- Transverse and Peninsula ly reaching heights of 53 to 61 m (175 to 200 ft) and Ranges 1220 to 3000 m (4,000 to 10,000 ft) Sierra San Pedro Martir 2150 to 2775 m (7,056 to 9,100 R) d.b.h. of 91 to 152 cm (36 to 60 in). Old trees oc- casionally exceed 500 years and, among associated species, are second only to giant sequoia in volume. Climate For products requiring large, clear pieces or high dimensional stability, sugar pine’s soft, even- Temperature and precipitation vary widely grained, satin-textured is unsurpassed in throughout the range of sugar pine. For equivalent quality and value. The huge, asymmetrical branches latitudes, temperature decreases and precipitation high in the crowns of veteran trees, bent at their tips increases with elevation, and for equivalent eleva- with long, pendulous cones, easily identify sugar tions, temperature increases and precipitation pine, which “more than any other tree gives beauty decreases from north to south. Patterns unifying this and distinction to the Sierran ” (25). variability are relatively warm, dry summers and cool, wet winters. Precipitation during July and August is usually less than 25 mm (1 in) per month, and summertime relative humidities are low. Al- Habitat though water stored in snowpacks and soils delays the onset and shortens the duration of summer Native Range drought, evaporative stress often becomes great enough to arrest growth in the middle of the season (15). Most precipitation occurs between November Sugar pine (fig. 1) extends from the west slope of and April, as much as two-thirds of it in the form of the Cascade Range in north central to the snow at middle and upper elevations (26). Within its Sierra San Pedro Martir in Baja (ap- natural range, precipitation varies from about 840 to proximate latitude 30” 30’ to 45” 10’ N.). Its distribu- 1750 mm (33 to 69 in). Because winter temperatures tion is almost continuous through the Klamath and are relatively mild and seldom below freezing during and on west slopes of the Cas- the day, considerable photosynthesis and assimila- cade Range and , but smaller and tion are possible during the dormant season, at least more disjunct populations are found in the Coast partially offsetting the effects of summer drought Ranges of southern Oregon and California, (15). Transverse and Peninsula Ranges of southern California, and east of the Cascade and Sierra Soils and Topography Nevada crests. Its southern extremity is an isolated population high on a plateau in the Sierra San Pedro Sugar pine grows naturally over a wide range of Martir in Baja California. Over 80 percent of the soil conditions typically associated with - growing stock is in California (49) where the most hardwood . Soil parent materials include rocks extensive and dense populations are found in mixed of volcanic, granitic, and sedimentary origin and conifer forests on the west slope of the Sierra their metamorphic equivalents and are usually not Nevada. of critical importance. Soils formed on ultrabasic in- In elevation, sugar pine ranges from near sea level trusive igneous rocks such as peridotite and serpen- in the Coast Ranges to more than 3000 m (10,000 R) tinite, however, have low calcium-to-magnesium in the Transverse Range. ratios and usually support open conifer stands of Elevational limits increase with decreasing inferior growth and quality Nevertheless, sugar pine latitude, with typical ranges as follows: is often the dominant conifer on the more mesic of these sites (39,&j. Because site productivity is a function of several The authors are Geneticist, Pacific Southwest Forest and Range environmental variables-edaphic, climatic, and Experiment Station, Berkeley, CA, and Nurseryman, El Dorado biotic-it is difficult to relate parent material groups National Forest, Placerville, CA. or particular soil series with specific productivity

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classes, especially when they span wide ranges of elevation and latitude. Other factors being equal, the main edaphic influences on conifer growth are soil depth and texture, permeability, chemical charac- teristics, and drainage and runoff properties (5). The most extensive soils supporting sugar pine are well drained, moderately to rapidly permeable, and acid in reaction. Soils derived from ultrabasic rocks are very slightly acid to neutral (pH 7.0). In general, acidity increases with soil depth. Several edaphic properties are influenced by the degree of soil profile development. Soil porosity, permeability, and infiltra- tion rate decrease with more developed profiles, while water-holding capacity, rate of run-off, and vul- nerability to compaction increase. Sugar pine reaches its best development and highest density on mesic soils of medium textures (sandy loam to clay loams) but ranges into the lower reaches of frigid soils when other climatic variables are suitable. These soils are found most commonly in the order Ultisols and Alfisols. The best stands in the Sierra Nevada grow on deep, sandy loam soils developed from granitic rock. In the southern Cas- cade Range the best stands are on deep clay loams developed on basalt and rhyolite. In the Coast Range and Siskiyou Mountains in California and Oregon, the best stands are on soils derived from sandstone and shale. Much of the terrain occupied by sugar pine is steep and rugged. Sugar pines are equally distributed on all aspects at lower elevations but grow best on warm exposures (southern and western) as elevation in- creases. Optimal growth occurs on gentle terrain at middle elevations.

Associated Forest Cover

Sugar pine is a major timber species at middle elevations in the Klamath and Siskiyou Mountains, Cascade, Sierra Nevada, Transverse, and Peninsula Ranges. Rarely forming pure stands, it grows singly or in small groups of trees. It is the main component in the forest cover type Sierra Nevada Mixed Conifer (Society of American Foresters Type 243) (10) generally comprising 5 to 25 percent of the stocking. It is a minor component in 10 other types:

207 Red Fir 211 White Fir 1984 B 229 Pacific Douglas-Fir

0 100 200 23 1 Port-Orford-Cedar I I I I I I II 11 11 232 Redwood 1"'1"'1"'11"1~"1~"1 234 Douglas-Fir-Tanoak-Pacific Madrone 0 100 200 300 400 500 600 KILOMETERS 244 Pacific Ponderosa Pine-Douglas-Fir 246 California Black Oak Figure l-The native range of sugar pine. 247 Jeffrey Pine

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249 Canyon Live Oak

In the northern part of its range, sugar pine is commonly associated with Douglas-fir (Pseudotsuga menziesii), ponderosa pine (), grand fir (Abies grandis), incense-cedar (Calocedrus decur- rens), western hemlock (Tsuga heterophylla), western redcedar (Thuja plicata), Port-Orford-cedar (Chamaecyparis lawsoniana), tanoak (Lithocarpus densiflorus), and Pacific madrone (Arbutus men- ziesii). In the central part it is associated with ponderosa pine, Jeffrey pine (), white fir (), incense-cedar, California red fir (A. magnifica), giant sequoia (Sequoiadendron gigan- teum), and California black oak (Quercus kelloggii). Farther south, the usual associates are Jeffrey pine, ponderosa pine, (Pinus coulteri), in- cense-cedar, white fir, and bigcone Douglas-fir (Pseu- dotsuga macrocarpa). At upper elevations Jeffrey pine, (Pinus monticola), Califor- nia red fir, and lodgepole pine (P contorta) grow with sugar pine. In the Sierra San Pedro Martir, Jeffrey pine and white fir are the main associates. Common brush species beneath sugar pine include greenleaf manzanita (Arctostaphylos patula), deerbrush (), snowbrush (C. velutinus), mountain whitethorn (C. cordulatus), squawcarpet (C. prostratus), bearclover (Chamaebatia foliolosa), bush chinkapin (Castanop- sis sempervirens), bitter cherry (Prunus emarginata), salal (Gaultheria shallon), coast rhododendron (Rhododendron californicum), and gooseberries and currants in the genus Ribes (11). From a silvicultural standpoint, Ribes spp. are especially important be- cause they are alternate hosts to the white pine blister fungus ( ribicola). At least 19 different species grow in the Mixed Conifer Type, of which the Sierra gooseberry (R&s roe&i) is most prevalent on more xeric, upland sites, and the Sierra currant (R. nevadense) on more mesic sites (35).

Life History

Reproduction and Early Growth Figure 24iugar pine cones.

Flowering and Fruiting-Sugar pine is monoe- cious. Reproductive buds are set in July and August 12 months after pollination. By this time, the is but are not discernible until late in the next spring. at its final size with a fully developed coat. Conelet Time of pollination ranges from late May to early elongation continues during the second season until August, depending on elevation, and to a lesser ex- maturation in late summer. Mature sugar pine cones tent on latitude. (fig. 2) are among the largest of all , averag- Female strobili are 2.5 to 5.0 cm (1 to 2 in) long at ing 30 cm (12 in) and ranging up to 56 cm (22 in) time of pollination and double in size by the end of long. Dates of cone opening range from mid-August the growing season. Fertilization of eggs by male at low elevations to early October at high elevations gametes takes place late the following spring, about (12,19,32).

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Cone production starts later and is less prolific in Seedling DevelopmentSugar pine show sugar pine than in its associates. During a 16-year dormancy, which can be readily broken by stratifica- study in the central Sierra, fewer than 5 percent of tion for 60 to 90 days or by removal of the seed coat sugar pines less than 20 cm (8 in) in d.b.h., and 50 and inner papery membrane surrounding the seed. percent less than 31 cm (12 in) in d.b.h., produced Germination of fresh seed is uniformly rapid and cones. Of trees 51 cm (20 in) or more, 80 percent high, exceeding 90 percent if adequately ripened, produced cones, and dominant trees produced 98 per- cleaned, and stratified. Viability may decline rapidly cent of the total. Intervals between heavy cone crops with time in storage at temperatures above freezing, averaged 4 years and ranged from 2 to 7 (12). but deep-frozen seed maintains viability much longer Loss of sugar pine cones is heavy; the probability (1,32,47). of a pollinated conelet developing to maturity is only On unprepared seed beds, seed-to-seedling ratios 40 to 50 percent. Predation by the sugar pine cone are high (244 to 483). Soil scarification reduced the ratio to 70 in one case, and scarification with rodent beetle (Conophthorus Zambertianae) can cause up to poisoning dropped it to 38 in another (12). 93 percent loss. Douglas squirrels and white-headed Seedling losses are continual and only 20 to 25 woodpeckers also take a heavy toll (7,11,17). percent of the initial germinants may survive as long Spontaneous abortion of first-year conelets is high. as 10 years. Drought may kill up to half of the first- Observations of control-pollinated trees in the year seedlings. Cutworms and rodents, which eat showed that 19 percent of seeds still attached to seedling , also take female strobili were lost 5 to 12 weeks after bagging, their toll (11,12). Seedlings infected by blister rust with no obvious signs of insect or pathogen-caused rarely survive more than a few years. damage (41). The amount of abortion varied from 15 Germination is epigeal(32). Seedlings rapidly grow to 85 percent among trees, for both bagged and un- a deep taproot when seeds germinate on bare bagged strobili. Since this pattern was consistent in mineral soil. In one comparison, taproots penetrated successive years, a genetic cause was suggested. to an average depth of 43 cm (17 in) on a bare sandy soil, but only half as deep when the soil was overlain Seed Production and Dissemination-Mature with duff (11). Lateral roots develop near and paral- trees produce large amounts of sound seeds. In a lel to the soil surface, often growing downward some study of 210 trees in 13 stands in the central and distance from the stem. In heavier, more shallow northern Sierra Nevada, the average number of soils, laterals are often larger than taproots. During sound seeds per cone was 150, with individual trees the second season, laterals commonly originate on ranging from 34 to 257. Higher numbers of seeds per the lower taproot and occupy a cone of soil which has cone (209 to 219) have been reported, but whether its base at the tip of the taproot. After 2 years on the count was based on sound or total seeds was not three different soil types in Oregon, the taproots of specified. In good crop years, the proportion of sound natural sugar pine seedlings ranged from 56 to 102 seeds is usually high (67 to 99 percent) but in light cm (22 to 40 in), were significantly deeper than those crop years can fall as low as 28 percent (7,121. of Douglas-fir and grand fir, but shorter than those Cones are ripe and start to open when their color of ponderosa pine and incense-cedar. Lengths of main turns light brown and specific gravity (fresh weight lateral roots showed the same species differences. Top-to-root ratios for sugar pine ranged from 0.17 to basis) drops to about 0.62. Seed shed may begin in 0.28 (length) and from 1.33 to 1.60 (dry weight) (46). late August at low elevations and at higher eleva- Seasonal shoot growth starts later and terminates tions is usually complete by the end of October (11). earlier in sugar pine than in its usual conifer as- Seeds are large and heavy, averaging 4,630 seeds sociates, except white fir. At middle elevations in the per kilogram (2,1OO/lb). Since their wings are rela- central Sierra Nevada, shoot elongation begins in tively small for their size, seeds are not often dis- late May, about 2 weeks after ponderosa pine and a persed great distances by wind, and 80 percent fall month before white fir, and lasts about 7 weeks. within 30 m (100 R) of the parent tree. Birds and Radial growth begins about 6 weeks earlier than small mammals may be an important secondary shoot growth and extends throughout the summer mechanism of dispersal, even though they consume (11). most of the seeds they cache. In good seed years, Planting of sugar pine has not been so easy or large amounts of seed fall, with estimates ranging successful as for some of the yellow pines. Although from 86,500 to more than 444,80O/ha (35,000 to reasons for the many recorded failures are often com- 180,00O/acre) in central Sierra Nevada stands plex, lower drought tolerance may be one of the fac- (11,32). tors. During natural regeneration, the ability of

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sugar pine seedlings to avoid summer drought by rapidly growing a deep taproot largely compensates for the relative intolerance of tissues to moisture stress (38). To survive the first summer after planting, seed- lings must have the capacity to regenerate vigorous new root systems. For other western conifers, root growth capacity is conditioned by particular com- binations of nursery environment and time in cold storage after lifting; these requirements are species and seed-source specific (22,24,38). Although pat- terns of root growth capacity have not been worked out for sugar pine, it is clear that amounts of root growth are substantially less for sugar pine than for its associates (23). Early top growth of sugar pine is not so rapid as that of western yellow pines, and l-year stock is too small for planting when seed is sown in May, for years the tradition in California nurseries. Root dis- eases, to which young sugar pines are unusually vul- nerable, can compound the problem by weakening seedlings that survive, thus reducing their chances of establishment on the site. Sowing stratified seed in February or March extended the growing season and produced healthy seedlings of plantable size in one season (23). A more expensive alternative to bareroot stock that holds some promise is con- tainerized seedlings grown under accelerated growth regimes (28).

Vegetative Reproduction-Sugar pine does not sprout, but young trees can be rooted from cuttings. The degree of success is apparently under strong genetic control. In one trial the proportion of cuttings that rooted from different ortets from 3 to 6 years old ranged from 0 to 100 percent (27). As for most con- ifers, rootability diminishes rapidly with age of donor tree. Grafts, however, can be made from donors of all ages, with success rates from 70 to 80 percent com- mon. Problems of incompatibility, frequent in some species such as Douglas-fir, are rare in sugar pine.

Sapling and Pole Stages to Maturity

Growth and Yield-Veteran sugar pines (fig. 3) often reach great size. Large trees have commonly scaled 114 to 142 m3 (20,000 to 25,000 fbm, Scribner log rule), with a record of 232 m3 (40,710 fbm). A “champion,” located on the North Fork of the Stanis- laus River in California, measured 65.8 m (216 ft) tall and 310 cm (122 in> in d.b.h., but trees up to 76 m (250 ft) tall have been reported (11,36). These and previous champions of this century are dwarfed by the first sugar pine measured by David Douglas and Figure 3-Mature sugar pine. (Courtesy of Western Wood Products described in his diary (37): “Three feet from the ASSOC ., Portland, OR.)

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ground, 57 feet 9 inches in circumference; 134 feet Reaction to Competition-Sugar pine tolerates from the ground, 17 feet 5 inches; extreme length 215 shade better than ponderosa pine but is slightly less feet.” tolerant than incense-cedar and Douglas-fir and Early growth of sugar pine is slow compared with much less so than white fir (14). A seral species, it ponderosa pine, but growth rates accelerate in the becomes less tolerant with age, and overtopped trees pole stage and are sustained for longer periods than decline unless released (11). Thus, dominant sugar those of common associates. Consequently, sugar pines in old-growth stands were probably dominant pines are usually the largest trees, except for giant from the start, or released by natural causes early in sequoia, in mature and old-growth stands. On better life. White fir would usually be the climax species in sites annual growth increments in basal area of 2.5 mixed conifer forests in the absence of any natural percent and more can be sustained up to stem disturbance; however, fire, insects, disease, and other diameters of 76 to 127 cm (30 to 50 in) or for 100 to agents are natural and pervasive features of these 150 years (11). Growth of sugar pine is best between forests. Such disturbances frequently cause gaps, in which the relatively tolerant sugar pine is adapted 1370 and 1830 m (4,500 and 6,000 ft) in the central to grow (14). For these reasons, sugar pine is often Sierra Nevada, between the American and San Joa- adapted to regenerate in a shelterwood silvicultural quin Rivers. system (33). In young mixed conifer stands, sugar pine often Competition from brush severely retards seedling constitutes a relatively small proportion of the total establishment and growth. Only 18 percent of seed- basal area but contributes disproportionately to lings starting under brush survived over a period of growth increment. On the El Dorado National Forest 18 to 24 years, and after 10 years the tallest seed- in the western Sierra Nevada, in stands ranging in lings measured were only 29 cm (11.4 in). Given an age from 50 to 247 years, the sugar pine component even start with brush, however, seedlings can com- was only 6 to 7 percent (range: 3 to 14 percent) of pete successfully (11). the average basal area, but its average annual basal Light shelterwoods can protect seedlings of sugar area growth was 11.3 percent (range: 2 to 35 percent) pine and white fir against frost, which seldom affects of the stand total. A similar relationship was found ponderosa and Jeffrey pines, and provide them with on the Plumas National Forest in the northern Sier- a competitive advantage because of their greater ra Nevada: in stands from 58 to 95 .years old, average tolerance to shade (13,43,44). On the other hand, basal area of sugar pine was 7 percent (3 to 16), but young sugar pines stagnate beneath an overstory and lo-year growth was more than 12 percent (6 to 19). in competition with root systems of established trees Ten-year volume increment in mixed conifer stands or brush. But because they respond well to release, from 40 to 80 years old was greater for sugar pine the basal area increment of sugar pines is often than for Douglas-fir, white fir, ponderosa pine, and double that of companion species after heavy thin- incense-cedar in each of five basal area categories (9). nings (33). Thus, skill in the amount and timing of Mean increment for sugar pine was 4.1 percent, com- overstory removal is a key factor in successful sil- pared to 3.1 percent for all others. vicultural management of sugar pine. Yields of sugar pine are difficult to predict, because Sugar pine does not self-prune early, even in dense it grows in mixes of varying proportion with other stands, and mechanical pruning is necessary to en- species. In the old-growth forest, the board foot sure clear lumber of high quality. volume of sugar pine was 40 percent of total in Damaging Agents-The pathology of sugar pine stands dominated by ponderosa pine and sugar pine. is dominated by white pine blister rust, caused by In exceptional cases on very small areas, yields were , a disease serious enough to 2688 m3/ha (192,000 fbmacre) (11). Yield tables for severely limit natural regeneration in areas of high young growth are based on averages for all commer- hazard, and thereby alter successional trends. cial conifers and assume full stocking (8). The data Among commercially important North American base is limited, so the tables are at best a rough white pines, sugar pine is the most susceptible. In- guide. Realistically, yields may reach 644 m3/ha fected seedlings and young trees are inevitably killed (46,000 fbm/acre) in 120 years on medium sites, and by cankers girdling the main stem. up to 1190 m3/ha (85,000 fbmacre) in 100 years on Blister rust was introduced into western North the best sites, with intensive management (11). America shortly after the turn of the century at a single point on Vancouver Island and has since Rooting Habit-Sugar pine develops a deep spread eastward throughout the Inland Empire and taproot at an early age. south through the Cascade, Klamath, North Coast,

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and Sierra Nevada Ranges. It has not yet been found widespread, are usually at endemic levels. Several in the Transverse or Peninsular Ranges of southern trunk and butt rots attack sugar pine but are usually California, even though alternate host species are confined to mature and overmature trees (2,21). abundant there. Within the range of sugar pine, con- Several root and damping-off pathogens cause ditions for infection are not nearly so uniform as for severe damage to sugar pine in nurseries, with an- western white pine in the Inland Empire. Incidence nual losses up to 50 percent (45). In approximate and intensity of infection on sugar pine are highest order of importance, these are Fusarium oxysporum, in Oregon and northern California and become Macrophomina phaseoli, and species of Pythium, progressively less to the south, as climate becomes Phytophthora, and Rhizoctonia. In addition to caus- warmer and drier. Within any area, however, hazard ing direct losses in the nursery, these diseases may varies widely and depends on local site conditions. reduce field survival of planted seedlings in more These are complex, but two of the most important stressful environments by causing stunting and factors are the duration of moisture retention on chlorosis. Nursery fumigation controls most of the foliage following rain, fog, or dew, and the distribu- organisms involved but is least effective on tion and density of the alternate hosts, currant and Fusarium. A simple and promising alternative con- gooseberry bushes (Ribes spp.). Thus, cool north trol method is early sowing of stratified seed. Soil slopes are more hazardous than warm south slopes, temperatures in late winter and early spring permit and relatively humid stream bottoms and lakesides seed germination and root development but are still are more hazardous than upland sites. In the Cas- cool enough to inhibit fungal growth. cade Range and Sierra Nevada of northern Califor- Sugar pine hosts many different insects, but the nia, infection averaged two to three times higher ( ponderosae) is of near stream bottoms than on adjacent slopes (4). overwhelming importance. This insect can cause Attempts to control blister rust by chemical widespread mortality, often killing large groups of therapy or eradicating alternate hosts have been trees (48). Several other bark-feeding insects con- abandoned as impractical and ineffective. Except on tribute directly or indirectly to mortality in sugar highly hazardous sites, sugar pine in natural stands pines, particularly after periods of drought. Death can be effectively managed by judiciously selecting results from predisposing trees to mountain pine leave trees with cankers relatively far from the bole beetle. The red turpentine beetle (Dendroctonus and by pruning cankers in the lower crown (4). ualens) is usually restricted to small areas near the Plantations are a much more serious problem. The root crown but during drought may extend two or microenvironmental changes on a site following more meters up the bole, destroying the entire cam- clearcutting-including dew formation on foliage and bium. The California flatheaded borer (Melanophila the rapid regeneration of alternate host Ribes spp.- californica) usually attacks decadent and unhealthy greatly augment the probability of rust intensifica- trees, but trees under heavy moisture stress are also tion and spread on both hosts. Uniform age and vulnerable. The California fivespined ips (Zps stocking make sugar pine plantations vulnerable to paraconfusus) is only capable of penetrating thin nearly total destruction for 20 years or longer. bark in sugar pine. Small trees are often killed, but Genetically resistant sugar pines in mixture with large trees only top-killed (16). other conifers offer the most promising solution. The sugar pine cone beetle (Conophthorus lamber- Dwarf mistletoe ( californicum) may tianae) can be extremely destructive to developing seriously damage infected trees by reducing growth second-year cones, destroying up to 75 percent of the in height, diameter, and crown size, and predisposing crop in some years. Since stunted cones are apparent weakened trees to attack by bark beetles. Extending by mid-June, the extent of the crop loss can be as- throughout the range of sugar pine, except for iso- sessed well before cone collection. The sugar pine lated stands in Nevada, the south Coast Ranges of scale (Matsucoccus paucicicatrices) occasionally kills California, and Baja California, this mistletoe was foliage and branches, predisposing trees to bark found in only 22 percent of the stands examined and beetle attack. The dead “flags” resulting from heavy on only 10 percent of the trees in those stands. attack mimic advanced symptoms of white pine Spread is slow and can be controlled by sanitation blister rust. Occasionally, the black pineleaf scale cutting (20,42). (Nuculaspis californica) defoliates sugar pine at mid- A needle cast caused by Lophodermella arcuata is crown, weakening the tree. These scale attacks are occasionally and locally damaging. Root diseases often associated with industrial air pollution or caused by mellea, Heterobasidion an- heavy dust deposits on foliage (16). nosum, and Verticicladiella wageneri are capable of Among its coniferous associates, sugar pine is the killing trees of all ages and sizes but, though most tolerant to oxidant air pollution (34), while in- Pinus lambertiana

termediate in fire tolerance (39) and frost tolerance from southern California to southern Oregon, showed (43,44). It is less tolerant of drought than most com- simiIar trends (27). Greatest growth was expressed panion species with which it has been critically com- in seedlings from intermediate elevations in the pared, including knobcone (Pinus attenuata) and central Sierra Nevada, a result consistent with ob- Coulter pines (50,511, ponderosa pine, Douglas-fir, servations in natural stands. Thus, genetic adapta- incense-cedar, and grand fir (40). tion to climatic variables associated with elevation is clearly evident in sugar pine, requiring a close match between seed source and planting site in artificial Special Uses regeneration. The degree of variability expressed among progenies of different seed parents within Upper grades of old-growth sugar pine command seed collection zones indicates that selection for rapid premium prices for specialty uses where high dimen- early growth should be effective. sional stability, workability, and affinity for glue are Resistance to white pine blister rust is strongly essential. The wood is light (specific gravity, 0.34 inherited, and three different kinds have been recog- + 0.03) (3), resists shrinkage, warp, and twist, and is nized (29). A rapid, hypersensitive reaction to invad- preferred for finely carved pattern stock for ing mycelium is conditioned by a dominant gene. machinery and foundry casting. Uniformly soft, thin- This gene, which occurs at variable but relatively low celled spring and summer wood and straight grain frequencies throughout the range of sugar pine, is account for the ease with which it cuts parallel to or highly effective against most sources of inoculum. A across the grain, and for its satin-textured, lustrous race of blister rust capable of overcoming this gene finish when milled. Its easy working qualities favor was discovered in a plantation in the Klamath Moun- it for molding, window and door frames, window tains (30), but evidently had not spread from this site sashes, doors, and other special products such as 10 years after it was found (31). In certain families, piano keys and organ pipes. Wood properties of another kind of resistance is expressed by slower young growth are not so well known. Pruning would rates of infection and mortality, fewer infections per undoubtedly be required to produce clear lumber tree, and by a higher rate of abortion of incipient during short rotations. infections. This “slow rusting” is apparently inherited quantitatively and, while less dramatic than single gene resistance, may be more stable to variation in Genetics the pathogen in the long term. Probably two or more generations of selection and breeding will be neces- Sugar pine is one of the more genetically variable sary to accumulate enough genes in parental stock members of the genus. Average heterozygosity of to make this kind of resistance usable in commercial specific genes coding for seed proteins (isozymes) was silviculture. A third kind of resistance is age-depend- 26 percent, a value near the upper range (0 to 36 ent. In common garden tests, infection among grafted percent) of pines studied so far (6). How adaptive clones from mature trees ranged from 0 to 100 per- variation is distributed over the range of environ- cent, yet offspring from the apparently resistant ments encountered in over 14” of latitude and 2000 clones were fully susceptible. Although not under- m (6,560 ft) of elevation is largely unknown, however, stood, the mechanisms and inheritance of mature because of a lack of field data from provenance or tree resistance are very strong and could play a sig- progeny tests. nificant role in stabilizing resistance over a rotation. In a 3-year nursery trial, pronounced differences Since all three kinds of resistance are inherited in- in height and diameter growth were found among dependently, there is a real promise for an enduring seedlings of five seed sources sampled along an and well-buffered genetic control of this most elevational transect on the west slope of the Sierra destructive disease. Nevada (18). The fastest growing seedlings were from the lower-middle elevation (1100 m or 3,595 R) and were twice the height of those from the highest Hybrids elevation (2195 m or 7,200 ft). Except for the source from the lowest elevation (770 m or 2,525 ft), which Barriers to crossing with other white pines are ranked second, growth varied inversely with eleva-’ very strong in sugar pine (7). No natural hybrids are tion. Elevation of the seed source accounted for 52 known and repeated attempts to cross sugar pine percent of the total variance among seedlings, and with other North American white pines have failed. the component of variance for families within stands Small numbers of F1 hybrids were made with two was a substantial 16 percent. More comprehensive Asiatic white pines, however: Korean pine (Pinus nursery trials, of families from seed parents ranging koraiensis) and Armand pine (I? armandii). These

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species are of silvicultural interest because of their 13. Fowells, H. A., and N. B. Stark. 1965. Natural regeneration relative resistance to blister rust. Mass production of in relation to environment in the mixed conifer forest type of Fi seed is probably impractical because of low seed California. USDA Forest Service, Research Paper PSW-24. set, but backcrosses of I? lambertiana x armandii to Pacific Southwest Forest and Range Experiment Station, sugar pine have yielded abundant sound seed. In Berkeley, CA. 14 p. and C. T. Dyrness. 1973. Natural limited field tests, the backcross progenies were more 14. Franklin, Jerry F., vegetation of Oregon and . USDA Forest Service, resistant than intraspecific crosses of the same sugar General Technical Report PNW-8. Pacific Northwest Forest pine parents. By using a broader genetic base of P. and Range Experiment Station, Portland, OR. 417 p. armandii, resistance in the backcross could be im- 15. Franklin, J. F., and R. H. Waring. 1980. Distinctive features proved. of the northwestern coniferous forest: development, structure, and function. In Proceedings, Fortieth Colloquium on Forests: Literature Cited Fresh Perspectives from Ecosystem Analysis, 1979, Corvallis, OR. p. 59-86. Oregon State University, Corvallis. 16. Furniss, R. L., and V. M. Carolin. 1977. Western forest 1. Baron, F. J. 1978. Moisture and temperature in relation to insects. U.S. Department of Agriculture, Miscellaneous seed structure and germination of sugar pine (Pinus Publication 1339. Washington, DC. 654 p. Zumbertiana Dougl.). American Journal of Botany 65:804-810. 17. Hall, R. C. 1955. Insect damage to the 1954 crop of Douglas-fir and sugar pine cones and seeds in northern 2. Bega, Robert V., tech. coord. 1978. Diseases of Pacific Coast conifers. U.S. Department of Agriculture, Agriculture California. USDA Forest Service, Miscellaneous Paper Handbook 521. Washington, DC. 206 p. PSW-18. Pacific Southwest Forest and Range Experiment 3. 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